Generally speaking, a process is required to complete the design of a product, in which two-dimensional drawings are prepared and the manufacturing of a trial product with them and testing are performed to dig out its defects, followed by the update of the drawings for further maturity. However, as the iteration of trial requires a large amount of development time and trial cost, in recent years it has been tried to reduce the development time utilizing the analytical technique of CAE (Computer Aided Engineering).
The product design flow with the prior CAE analysis is described as follows. FIG. 2 is a figure showing the flow diagram for a product design with the prior CAE analysis.
A designer prepares two-dimensional layout drawings or a three-dimensional layout model with a CAD (Computer Aided Design) system (S100). Then, a three-dimensional rough model is prepared for each or some parts in the three-dimensional CAD system (S101), and a CAE analysis such as stress analysis etc. is performed for the rough model (S102).
As a result of the CAE analysis, if the defects such as the lack of product strength are found (S103), the layout will be corrected (S104). The two-dimensional drawings, on which the detail dimensions and process directions are shown, are prepared according to the corrected layout (S105), and a trial product is manufactured on the basis of the two-dimensional drawings. In the case of aluminum alloy casting parts, the trial manufacturing is generally conducted with a sand mold. A trial product of sand mold is made in the following steps: the manufacturing of a male wooden mold for sand mold (S106), the manufacturing of a female sand mold (S107), casting with the sand mold and finishing the product with machining (S108).
The trial product undergoes required tests (S109) and the two-dimensional drawings are corrected reflecting the test results.
If the trial product of sand mold is not ascertained to reach the expected product maturity level, the steps S105 through S109, from the trial manufacturing to the test with the trial product of sand mold, will be iterated. If it is judged that the trial product has the prospects of satisfying the expected product maturity level, the mass production with a metal mold will be started. For manufacturing the metal mold, a three-dimensional CAM model is prepared (S110), with which a three-dimensional metal mold model is prepared for the mold manufacturing (S111). The metal mold is manufactured with the three-dimensional metal mold model data (S112). The tests before the mass production are performed for the mass production confirmation product manufactured with the metal mold (S113), and if the defects are found out (S114), the two-dimensional drawings are again corrected (S115), and the three-dimensional CAM model is corrected accordingly (S116) to iterate the steps (S115, S116, S111 through S114) till the defects disappear. If no defects are found (S114), the mass production drawings will be prepared to start the mass production.
The rough model represents the final shape of product roughly, omitting small ribs, thinning, draft angles and fillets. It means that the three-dimensional model of the rough model cannot be applied to the machining data for the mold manufacturing. The reason why the rough model was used in the prior CAE analysis is that the CAM model, the data of which deserved to be applied to the machining data of the mold manufacturing, could not be brought into use in the actual development. It was extremely difficult to divide the CAM model into meshes due to its data size and fineness, and it took too much time to perform the stress calculation etc. even if the mesh dividing was performed successfully.
Metal molds are much more expensive than sand molds, and it will be a great waste when such changes come up later that require more than the mold correction. It is the reason why sand molds have been used for aluminum alloy casting parts.
However, the development flow with CAE analysis mentioned before was not efficient in the following points.
The rough model did not incorporate the detailed shape of product, not allowing checking the effects of reinforcement with fillets and ribs to end up with many unanticipated defects in the trial product of sand mold sometimes. Therefore, the test of the trial product of sand mold was liable to be delayed, and it required several times of the iteration depending on the degree of completion.
The product manufactured with a sand mold generally weighs 10% more than that with a metal mold. It is attributed to the fact that the product has to be made thicker because the sand mold is inferior to the metal mold in the accuracy of shape and is not able to withstand the pressure. Therefore, the product of sand mold tends to have excessive strength than that of metal mold. In other words, the strength of the product is liable to be insufficient when it is manufactured with a metal mold. Unanticipated defects happened to emerge in the stage of mass production confirmation, which led to the correction or re-manufacture of metal mold, caused the increase in the development period of time and cost.
Further, the manufacturing of a wooden mold required another three-dimensional CAM model or some other approaches, since the trial product of sand mold was manufactured with the two-dimensional drawings. It took as many as one man-month to produce the three-dimensional CAE model with the rough model for an expert on CAE.
The object of the present invention to solve the problems described above is to provide a new design method to improve the flow of a product development with three-dimensional CAM model.